Light Emitting Diodes (“LEDs”) are commonly used as indicators in a variety of applications, ranging from consumer electronics (e.g., stereo status displays, power on/off indicators, etc.) to commercial applications such as in manufacturing control consoles, avionics, and surgical systems. However, commonly available LEDs, as known to those familiar with the art, are typically either single color, bi-color (two-bit color), or, more recently, tri-color (three-bit color) LEDs. Further, within these limited choices the colors themselves are limited to either red/green bi-color LEDs or red, green, and blue tri-color LEDs. The range of possible indications from the same LED and the ability to transmit information to a viewer through a multi-color display is thus limited by current LED technology.
Methods do exist for obtaining multi-color displays from either monochromatic display devices or from display devices with limited colors. Some methods have been applied to multi-color displays as well for achieving crisper displays. For example, temporal dithering has been used in Cathode Ray Tube (“CRT”) and Liquid Crystal Display (“LCD”) devices to improve half-toning and color resolution. This process of representing continuous tone images on, for example, a binary display device is known as “half-toning” or “dithering.”
Dithering works because the human visual system integrates information over spatial regions, so that a spatial pattern of light and dark can invoke a sensation approximating that of a uniform color area even when the individual display elements cannot be resolved. Temporal dithering is especially useful in the case of dynamically controllable displays such as CRTs and flat panel displays. Temporal dithering refers to the rendition of a desired gray level with a spatial distribution of flickering pixels. The response of the human visual system to color is markedly different than its response to chromatic or luminance information. For the purposes of dithering, the important facts are that the human chromatic sub-system is low pass both in space and time. For example, if a pattern of colored stripes is progressively minified, at some point the colors of the individual stripes will blend and the pattern will appear to have variations only of intensity. Further, the pattern will be completely invisible if the colors are made equally illuminate (equal visual intensities).
Additional benefits may be reaped from the temporal low pass character of the chromatic system. When two colored lights are exchanged or flickered, the color will appear to alternate at low flicker rates, but when the frequency is raised to 15-20 kHz, color-flicker fusion occurs, where a single steady color is seen and the flicker is seen as a variation of intensity only. It is possible to eliminate all sensation of flicker by balancing the intensity of the two lights (colors) making them equally illuminate. When the intensities are not balanced, the luminance flicker can be seen at frequencies as high as 50-60 kHz.
While it is desirable to have multi-color capable indicators for rapid and accurate transmission of information from an electronic system to an operator, the limitations of currently existing LED technology are such that only a limited number of colors can be usably achieved. Further, these existing displays are limited in that the color of each LED in a display cannot be changed beyond the current state of the art of three colors per LED (e.g., when using tri-color LEDs). Therefore, while it is desirable to have more than three colors available for display within the same or multiple LED indicators, it is not feasible using the currently available LED technology.
Therefore, a need exists for a method and system for temporal dithering of LED indicators to achieve multi-bit color resolution indicators that can reduce or eliminate the problems of limited display colors, non-chromatically adjustable displays, and other problems associated with prior art LED indicators.